Apparatus for recovering mixed salts from solution



N. T. BACON APPARATUS FOR RECOVERING MIXED SALTS FROM SOLUTION Original Filed Dec. 2'7, 1919 I v INVENTOR BY A.) ATTORNEY flaflcm Patented Dec. 1%, i924.

FFlCE.

NATHANIEL TERRY BACON, OF PEACE DALE, RHODE ISLAND, ASSIGNOR TO THE SOL- VAY PROCESS COMPANY, E SOLVAY, NEW YORK, A CORPORATION OF NEW YORK.

APPARATUS FOR RECOVERING MIXED SALTS FROM SOLUTION.

Original application filed December 27, 1919, Serial No. 347,832. Divided and this application filed April 7, 1922. Serial No. 550,840.

To all whom it may concern:

Be it known that I, NATHANIEL T. BACON, a citizen of the United States, residing at Peace Dale, in the county of Washington and 5 State of Rhode Island, have invented a new and useful Apparatus for Recovering Mixed Salts from Solution, of which the following is a specification.

My invention relates particularly to the recovery of ammonium chlorid from the mother liquors of the ammonia soda process, in which it is contained, together with varying quantities of sodium chloride and carbonate of ammonia, but practically free from other impurities. I

The recovery of the ammonium chlorid by boiling down the mother liquor is a matter of extreme diihculty, because of the dissociation of ammonium chlorid after the free ammonia has been driven off and the conse uent destructive corrosion of metallic sur aces, especially the heating pipes. Such part of the NH,C1 as does not break up tends to adhere to the heating tubes and thus re- 5 duce their efliciency to a small fraction of that of clean tubes.

The object of my improvements is to avoid these difiiculties and at the same time provide for the separate recovery of the ammonium chlorid and sodium chlorid con- 1 tained in the liquor treated. The invention will be best understood by reference to the accompanying drawing, which is a diagrammatic representation of an organization of a paratus which may be used for carrying t e invention into effect.-

Referring to the drawing, A, B, represent two towers located in operative relation, in the former of which the liquor to be treated is preheated, and in the latter is evaporated, so as to effect crystallization and precipitation of the contained salts. The preheating of the liquor in the preheating tower A, is efi'ected by steam generated in the evaporating tower, B, and collected under steam traps, T, T, whence it Ipasses by pipe p, p, to heating tubes or coi s H, located at corresponding levels in the tower, A. The tower, A, is provided with bafifles, C, C, to prevent as far as possible convection currents therein, and so arranged as, at the same time, to permit gases'set free in the sure of the column of liquor therein by means of live steam passing through a nest of heating pipes, I, located below the lowest bafie in the tower, A. The bottom of the tower, B, is located somewhat above the level of, the heating tubes, I, so that the pressure of the column of liquid in the tower, A, is enough greater than that in the tower, B, to prevent boiling of the li nor in the tower, A, when the liquor in the lower part of the tower, B, is raised to the boiling point under the existing pressure.

The operation of the device is as follows 2-- The 1i nor to be treated is admitted through pipe, 3), to the preheating tower, A, and passes downward therethrou h, being heated in its assage by steam rom the steam traps, T, in the evaporating tower, B. In the preheater, A, a large part of the free .ammonia and the CO in the liquor are driven off and bubble up past the bafll es, C. These gases will gradually accumulate in the feed at the topof the tower until they raise the strength of ammonia and CO in the feed to a point at which very rich gas will be given off at the exit, X, at thetop of the tower from which these gases can be carried back for use in the ammonia soda system, or they can be utilized in making commercial carbonate of ammonia, or otherwise, as desired. Enough free ammonia will, however, remain in the liquor in the preheater A, to prevent dissociation of ammonium chloride therein.

The continuous feed of liquor by pipe, '0,

to the upper part of tower, A, causes a con-i tinuous flow of liquor downward through tower A, and thence past the heating tubes, I, through pipe, P, to the bottom of tower, B, and upward therethrough.

As the preheated liquor enters the evapcrating tower, B, it has been heated to tae boiling point at this level by steam in the heating tubes, 1, located at the base otthe tower, A. There will, however, be no ioulmoved by washing.

B, it will meet crystals of NaCl falling from the upper levels, and will saturate itself therewith at once, so that it will immediately begin to throw down NaCl as it boils, but it will still be below saturation with NH ,C1. the solubility of which increases rapidly with increasing temperature.

The NaGl precipitated in the bottom of the tower, B, is drawn ed, as through pipe, D, by means of a steam aspirator,.S, to filter F. It will be free from NILCI except for adhering mother liquor which can be re- In the upper portion of the evaporating tower, B, NILCI only will be precipitated, since the rapidly decreasing temperature, due to relief of pressure, will throw down NH Cl far more rapidly than the precipitation caused by concentration of the solution, and the solubility of NaCl is increased so much by removal of NI-Ifll from solution that the solution as it approaches the top of the column recedes more and more from saturation with NaCl. The precipitated NH CI is caught in an inverted cone, t and carried ofi by steam aspirator, S, to a filter F. Between the zones in which NaCl, and NI-LCI are separately precipitated, both salts are precipitated together and these mixed salts are received in an inverted cone,

t located at such a point that none of-the mixed salts will pass down into that portion of the tower in which NaCl alone is precipitated. This point will ordinarily be at about one fourth the distance from the bottom of the tower, though this will vary with variations in the amount of NaCl in solution. The mixed salts collected in the inverted cone, It, may be carried by pipe, Ur, and steam aspirator S to a filter, F or they may be delivered directly into the preheating tower, A, at a point near the bottom thereof where they will redissolve as the solution is saturated with neither salt at this point.

The small amount of free ammonia remaining in the liquor as it enters the tower, B, will be driven off in the lower part of the tower and will pass overin the steam from the lowermost of the tra s, T, and will condense with the steam an be drawn off in the drip from which it can be recovered by distillation.

Any danger of destruction of the pipes by chlorine set free by dissociation of NH4Cl' above this point may be obviated by admitting ammonia to the tower, B, as from a tank, K, through pipes k, k. The excess ammonia will, as above stated, pass-over with the steam and be collected in and recovered; from'the drip.

As the liquor passes upward through the tower, B, it will continue to boilunder re ducing pressure and with decreased temperature. The steam generated, and collected under the traps, T, passes over to the heatingtubes of corresponding level in the preheating tower, A, until a polnt is reached Where the steam temperature is so near that of the liquor surrounding the condenslng tubeslthat it will not be condensed by the feed in the .tower, A. The steam from the traps above this point, as well as that from a the top of the .tower, B, is drawn oil and condensed by means of vacuum pumps and cold water condensers Snot shown in the drawing) as in the or inary vacuum processes. The unevaporated liquor is returned from the top of the tower B, as by pipe M, to tower, A, where it is mixed with fresh feed.

By means of my invention I am able to recover the ammonium chloride content of mother liquor of the ammonia soda process uncontaminated with other salts, and without injury to the apparatus employed, the advantages of which will be readily apparent to those skilled in the art.

I do not claim herein the process described, the same having been claimed in an application for Letters Patent filed December 27th, 1919, Serial No. 347,832, which has matured into Patent 1,416,772, May 23, 1922, of which this application is a division;

What I do claim as new and desireto secure by Letters Patent is 1. In an apparatus for separately recovering mixed salts from a solution thereof the combination of a continuous, vertically elongated evaporating tower, separate means for heating the solution. means for causing a continuous upward flow ofheated solution of progressively decreasing temperature through said tower and a series of collecting devices disposed one above the other in said tower and arranged to permit a continuous flow of solution through said tower and to separately collect the salts precipitated therein at different temperatures.

2. In an apparatus for separately recovering mixed salts from a solution thereof the combination of a preheating tower, a continuous, vertically elongated evaporating tower connected therewith, means for causing a downward flow of solution of progressively increasing temperature through the preheating tower, means for causing an upward flow of solution of progressively decreasing temperature through the evaporating tower and a series of collecting devices vertically disposed one above the other in the evaporating tower and arranged to permit a continuous flow of solution through said tower and to separately collect the several salts precipitated at different temperatures therein.

3. In an apparatus for separately recovering mixed salts from a solution thereof the combination of a preheating tower, an evaporating tower connected therewith, means for causin a downward flow of solution of progressively increasing temperature through the preheating tower, means for causing an upward flow of solution of progressively decreasing temperature through the evaporating tower, a series of collecting devices vertically disposed one above the other in the evaporating tower for separately collecting the several salts, a collector in the evaporating tower arranged to collect mixed salts and means for return-- ing the mixed salts from suchcollector to th preheating tower.

4. In an apparatus for separately recovering mixed salts from a solution thereof the combination of a preheating tower and means for causin a downward How of solution therethroug a continuous, vertically elongated evaporating tower connected therewith, means for causing a flow of solution from the preheating tower to the evaporating tower, means for causing an upward flow of solution vthrough the evaporating tower, means for" heating the solution in the preheating tower from the top downward with steam at progressively higher temperatures evolved in the evaporating tower and a series of collecting devices vertically disposed one above the other in the evaporating tower and arranged to permit a continuous flow of solution through said tower and to separately collect the several salts precipitated at different temperatures therein.

5. In an apparatus for separately recovering mixed salts from a solution thereof the combination of a preheating tower and means for causing a downward flow of solution therethrough, a continuous vertically elongated evaporating tower connected therewith, means for causing a flow of solution from the preheating tocver to the evaporating tower, means for causing an upward flow of the solution through the evaporating tower, means for separating steam at successive points in the evaporating tower, means for utilizing the steam generated in the evaporating tower to progressively heat the liquid in the preheating tower from the top downward and a series of collecting devices vertically disposed, one above another in the evaporating tower and arranged to permit a continuous flow of solution through said tower and to separately collect the several salts precipitated at different temperatures therein.

In testimony whereof I afiix my signature, this 1st day of April 1922.

NATHANIEL TERRY BACON. 

